This invention concerns an improvement in nebulizers used for production of aerosols of uniform solution concentration and particle size. Commercial nebulizers deliver an unstable output of aerosol spray, primarily due to changes in solution concentration. This unstable output originates from evaporation processes occurring within the nebulizer. Droplet evaporation can take place due to elevation of vapor pressure from curved surfaces internal to the nebulizer and also due to reduction in the dew point of the air stream used to atomize the solution when the air stream is expanded to atmospheric pressure. Such evaporation leads to a spectrum of droplet sizes, some of which pass through the nebulizer system with the remainder of the droplets returning to the solution reservoir. Since some of the solvent is evaporated and passed through the nebulizer, the remaining solution undergoes a continuous increase in concentration which causes a constantly changing aerosol output.
Various methods have been employed to solve this instability in aerosol output. These approaches have primarily been directed toward correction of the increasing solution concentrations arising from the evaporation processes. In H. L. Berke and T. E. Hull, American Industrial Hygiene Association Journal, 36, 43 (1975), an aerosolizer is described, which has the ability to compensate for changes in concentration and volume of solution by adjustments to the pressure and temperature of the air jet used to atomize the solution. This device produces a fluctuating nebulizer solution concentration but does yield a stable mean aerosol concentration. In K. E. Lauterbach, A. D. Hayes, and M. A. Coelho, A. M. A. Archives of Industrial Health, 13, 156 (1956), a device is described which circulates the solution to be atomized between an aspirating and storage reservoir, but the device has no provision to alleviate the detrimental effects evaporation has on the solution concentration. In B. Y. H. Liu and K. W. Lee, American Industrial Hygiene Association Journal, 36, 861 (1975), a device is described which supplies a constant flow of liquid to the nebulizer. Fresh liquid is constantly supplied to the atomizer and excess liquid collected is not recirculated; as a result, the system does produce a stable aerosol output. However, this device has relatively complicated components and does not conserve or use all of the aspirating solution. Therefore, there is currently no nebulizer which provides a non-fluctuating and uniform aerosol spray output without the use of complicated support systems.
It is therefore an object of the invention to provide a simple aerosol spray device for producing a uniform aerosol spray output.
It is an additional object of the invention to provide an aerosol spray device with a vacuum means applied to the makeup assembly which permits the level of the solution in the aspirating assembly to be adjusted with respect to the makeup solution to stabilize the aerosol output.
It is a further object of the invention to provide an aerosol spray device with the bottom of an air vent tube positioned within the makeup assembly such that the solution within the aspirating assembly is maintained at the same level as the bottom of the vent tube.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.